1. Field of the Invention
The present invention generally relates to signal filtering and restoring techniques and, more particularly, to a video signal filtering method and circuit for removing noise and providing clean information-bearing video signals.
2. Description of the Prior Art
Video signals frequently must be sent over transmission lines found in harsh environment where they are susceptible to the injection of noise, such as electromagnetic radiation (EMR). For example, high EMR levels are present in commercial and military aircraft and remotely piloted vehicles and around factory monitors, video manufacturing line inspection systems, and recreational vehicle video systems.
For instance, in carrying out testing of military weapons, video signals from various sources are recorded onboard a test aircraft for later analysis on the ground. In many of the test aircraft, the problem is that the video information has so much noise injected onto it that it becomes virtually unusable for analysis later. After a review of this problem was carried out, the conclusion was reached that the noise was mainly due to the presence of large electromagnetic fields in the wiring bundles through which the video signals are routed.
Several different approaches, such as use of filter capacitors and video isolation transformers, were tried in an attempt to solve this problem. However, unfortunately these approaches created other problems by removing the DC reference required to properly record the video signals and not saturate any buffer amplifiers. As a consequence, a need arose for a different way to solve this problem, one that would remove the noise and provide a clean buffered video signal for recorders, without introducing a new set of problems.